Cobalt (II) Schiff base complexes have been used as oxidation catalysts and for the selective enrichment of oxygen by making use of their ability to adsorb and desorb oxygen. However, if these complexes are brought into contact with protic compounds such as water or alcohols in the presence of oxygen, they are irreversibly oxidized to hydroxocobalt (III) Schiff base complexes which have little or no ability to serve as catalysts or to adsorb and desorb oxygen.
In response to this problem, attempts have been made to reactivate the hydroxocobalt (III) Schiff base complexes by reducing them into cobalt (II) Schiff base complexes. Nishinaga et al have proposed the use of alcohol as a reducing agent (see the preprint for the 34th Conference on Complex Salts sponsored by Japan Chemical Society, p.344, 1984).
However, the method of reducing hydroxocobalt (III) Schiff base complexes to cobalt (II) Schiff base complexes with an alcohol being used as a reducing agent has several disadvantages. First, the reducing agent is not reusable; also, in order to achieve a high reduction rate, this method requires the reducing agent to be used in a stoichiometrically excess amount, but the cobalt (II) Schiff base complex containing the residual reducing agent will not serve either as an oxidation catalyst or as an oxygen-adsorbing and desorbing medium, and hence must be freed of such excess reducing agent; furthermore, the hydroxocobalt (III) Schiff base complex has a fairly low solubility in alcohol, and thus a concentrated alcohol solution sufficient to be suitable for use in large-volume treatment cannot be prepared; still further, an additional step is necessary to separate the reduced complex from alcohol.